[boot] Add framebuffer progress bar

After exiting UEFI, the bootloader had no way of displaying status to
the user. Now it will display a series of small boxes as a progress bar
along the bottom of the screen if a framebuffer exists. Errors or
warnings during a step will cause that step's box to turn red or orange,
and display bars above it to signal the error code.

This caused the simplification of the error handling system (which was
mostly just calling status_line::fail) and added different types of
status objects.

src/boot/loader.cpp

@@ -8,6 +8,7 @@
 #include "fs.h"
 #include "memory.h"
 #include "paging.h"
+#include "status.h"
 
 namespace args = kernel::args;